Exploring the Psychological Foundations of Borderline Personality Disorder

Dahyun Kim

April 25, 2025

What is often labeled as “overthinking” in a relationship, such as being overly sensitive and showing signs of codependency, may seem like a simple matter of mindset and personality. However, these symptoms tend to be overlooked, as they might be an indication of the possibility of underlying conditions such as Borderline Personality Disorder, often known as BPD. Borderline Personality Disorder is a mental health condition marked by pervasive patterns of difficulty in regulating emotions, identity disturbance, impulsivity, and often unstable relationships. It causes diagnostic and therapeutic dilemmas in clinical practice as the symptoms often overlap with other mental disorders, such as anxiety or bipolar disorder. Despite the diagnostic dilemmas, there have been clinical trials and studies that have been done targeting the cause of the BPD: neurological and genetic factors. 

It has been theorized that people with BPD have problems in their function and development of a part of the brain. According to the National Health Service, people with BPD tend to have complications with serotonin, a neurotransmitter, a messenger chemical that transmits signals between brain cells. If the serotonin, which is in charge of controlling bodily functions such as sleep and emotions, alters levels, it can result in depression, aggression, and difficulty controlling destructive urges, leading to BPD. Another discovery through an MRI scan revealed that people with BPD had 3 parts of the brain (amygdala, hippocampus, orbitofrontal cortex) that were smaller than usual or had abnormal levels of activity. The amygdala, which plays a key role in regulating emotions—specifically negative emotions like fear, aggression, and anxiety—often showed heightened activity in individuals with BPD, resulting in symptoms such as black-and-white thinking. The hippocampus, in charge of controlling behavior and self-regulation, was found to be a cause of BPD, where individuals showed intensified symptoms in emotional dysregulation. Lastly, the orbitofrontal cortex, involved in planning and decision-making, appeared to be smaller in people with BPD, contributing to the impulsivity and difficulties in judgment that are often seen. These brain differences are believed to be shaped by early life experiences and may explain the challenges people with BPD face in regulating their mood and maintaining stable relationships. 

Genetics also plays a great role in the cause of BPD. A Swedish study presented in the paper “Familial risk and heritability of diagnosed borderline personality disorder: a register study of the Swedish population”, researched the statistics behind the genetic factors and risks contributing to the borderline personality disorder, asserting that “heritability was estimated at 46% (95% CI = 39–53)” (Skoglund et. al., 2019). The study was focused on family and twin studies, showing that BPD aggregates in families specifically, raising the cause of genetics to 72%. However, due to the various factors that were disregarded in this research, the cause of BPD being mostly genetic cannot be ensured, suggesting that deeper and closer study on BPD has to be done in order to correctly diagnose people in the future. 

While diagnosing Borderline Personality Disorder (BPD) can be challenging, it is up to each individual to seek help when they recognize something may be wrong. National Health Society also suggested that BPD is often linked to environmental factors such as experiencing emotional, physical, or sexual abuse, being exposed to prolonged fear or distress during childhood, facing neglect within the family, or growing up around individuals with severe mental health issues. Recognizing these contributing factors is a crucial step toward understanding the disorder and breaking the stigma surrounding it. With the right support, therapy, and resources, individuals with BPD can learn to manage their symptoms and lead fulfilling lives.